Having a career is a known reason behind why women put off having children, but it’s not just being employed and building a professional reputation that’s responsible, suggests a new study. It’s job insecurity.

Researchers in Australia cast doubt on the familiar idea that women delay starting a family out of some misguided notion that they can have it all by waiting. Instead, the study suggests, women shy away from having kids until they at least have something.

The scientists found that the likelihood that women were moms by the age of 35 was reduced for every year the women spent picking up work on a temporary or casual basis. (This is different from part-time work, which can be quite stable.) They even put a number on it: if the woman had worked as a temp for one year she was 8% less likely to be a mother by 35. If she had a temp job for three years, she was 23% less likely to have had a kid and if it was five years, the rate rose to 35%. This was true whether the women were educated or not.

“Our findings suggest that, regardless of their socioeconomic circumstances, women generally aspire to economic security prior to starting a family,” write the authors of the study which was published in Human Reproduction. “We are confident that childlessness is related to employment status, over and above any relationships with socio-economic circumstance,” says co-author Lynne Giles, a senior lecturer at the university. “We took the woman’s educational attainment and that of her partner into account in our analyses.”

Giles and her colleague Vivienne Moore studied data collected from a cohort of 663 women who were followed from their birth in an Adelaide hospital between 1973 and 1975. Interviews with the women three and a half decades later filled in gaps about their significant life events, and showed that economic stability was an important contributor to family-building. Adelaide is not Australia’s largest city, nor its most diverse, but the findings seem to echo trends in other western cities.

The findings suggest that the more job insecurity countries face as a result of recessions the smaller its next generation may be. And that could have significant consequences for social security as well. “We are not arguing for women to have lots of children,” says Giles. “[But] a Western population needs to have fertility levels at replacement rate if it is to care for its aging population and pay taxes for publicly funded programs.” Significant health issues can also arise when women get pregnant or give birth at an older age, which may add to health care costs.

The authors suggest that more family-friendly policies for temporary workers may mitigate the trend; even in Australia, where citizens enjoy universal health insurance, temp jobs provide no maternity leave. “Current policy responses generally provide financial and other support to parents after they have children; there remains a need to develop complementary policies to facilitate the ability of couples to commit to family formation,” Giles writes. Alternately, companies could be punished for populating too much of their workforce with temps.

Such policies would be far less likely in the U.S., which has maternity leave policies that are as primitive as those of Papua New Guinea—a country in which 85% of the labor force work the land—and is generally much more pro-business than most of its Western allies. In fact, many argue that the government benefits new mothers receive are what drive some poorer young women to have kids in the first place. But the findings might still hold true: when women have reliable jobs they tend to plan motherhood more carefully.